1. Field of the Invention
This invention relates, generally, to high-speed paper-handling machines. More particularly, it relates to an oscillator that rapidly taps items along their respective trailing edges as they are fed into a hopper.
2. Description of the Prior Art
Whenever items in a stack are removed one at a time from the bottom of the stack, the items often fail to advance toward the bottom of the stack under the influence of gravity as the lowermost item is removed. The items in the stack are easily stuck to the walls of the bin or hopper within which they are stacked. In the absence of a mechanical jostling means it is necessary for a human operator to jostle the stack to cause the items to fall. This creates problems because the vacuum shuttle feed at the bottom of the stack, or other item-removing means such as a spinning frictional belt, are required to operate under varying loads if the stack does not move downwardly in a uniform manner during machine operation. Varying loads prevent the item-removing means from operating in an optimal manner.
The prior art most relevant to the present invention is disclosed in U.S. Pat. No. 6,695,304 entitled “Vibrating Means For Aligning Envelopes In A Hopper” to the present inventor. In that inventive structure, a wedge-shaped member positioned at the bottom of an envelope hopper oscillates under the control of a friction shuttle feed so that it lifts and drops an edge of the envelopes with each reciprocation, thereby breaking the frictional bonds between contiguous envelopes. The entire stack of envelopes bounces during oscillation of the wedge-shaped member. This jostling is desirable because it breaks said frictional bonds between contiguous items and it helps stagger the sheets as they exit the hopper.
A vacuum shuttle feed is quite reliable but a vacuum must be turned on and off quickly as the shuttle reciprocates. When an item at the bottom of a stack is ready to be discharged therefrom, the vacuum is turned on, i.e., the item is exposed to a vacuum, and the shuttle moves forwardly to remove the item from the bottom of the stack. A gate at the leading end of the apparatus blocks an item on top of the bottom item from being carried forward by the shuttle. The vacuum is then turned off until the shuttle returns to the bottom of the stack.
The earlier design does not work well when the items being introduced into a hopper are warped because such warping can defeat the grabbing action of the vacuum. Warped items are not uncommon.
There is a need, therefore, for an item-jostling apparatus that does not require a vacuum shuttle feed. The needed apparatus would have utility even when the items being fed into or removed from a hopper are warped.
The needed apparatus should also stagger the items as the items approach a separator.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.